(1) Field of the Invention
The present invention relates to a technique of crystallizing an a-Si film using a laser beam in a silicon thin film having a bottom-gate structure.
(2) Description of the Related Art
There is, for example, a silicon thin-film transistor (TFT) device included in a liquid-crystal display device or an organic electroluminescence (EL) display device. A semiconductor layer (hereinafter referred to as silicon thin film) which is a channel portion of the silicon TFT device and which includes silicon, for example, is formed generally by noncrystalline (amorphous) or crystalline silicon thin film. It is preferable here that the silicon thin film that is the channel portion is formed of a crystalline silicon thin film that has a high mobility compared to amorphous silicon. Thus, in a manufacturing process, a noncrystalline silicon thin film included in the channel portion is formed and then the formed noncrystalline silicon thin film is crystallized, thereby forming a crystalline silicon thin film.
As a method of crystallizing the noncrystalline silicon thin film, there is, for example, a method of crystallizing with irradiation of a laser beam such as a green laser beam having a wavelength of 532 nm (see, for example, Non Patent Literature 1: 41.2: Micro Silicon Technology for Active Matrix OLED Display. [SID Symposium Digest of Technical Papers 38, 1370 (2007)]).
Non Patent Literature 1 discloses a technique with which, in a bottom-gate structure, an electrode in a bus line region is made to have an Mo and AlNd structure in two layers to be under a region not irradiated with a laser beam and an electrode under a region irradiated with the laser beam is made to be an Mo single layer.